1.创建类的两种方式

1.1 方式一

class Foo(object):
    name = 'abc'
    age = 20

    def fun(self):
        return 999


obj = Foo()
print(obj.name)
print(obj.fun())

1.2 方式二

# 类名 = type("类名", (父类,) , {成员} )
Foo = type('Foo', (object, ), {'age': 123, 'func': lambda self: 888})

obj = Foo()
print(obj.age)
print(obj.func())

2.type创建类

首先执行__new__创建类，然后再执行__init__。

class type:
    def __init__(self):
            在空值初识话数据

    def __new__(self):
            创建->创建类

2.1 创建自定义类前添加或删除类中元变量或方法

• 如果类继承时出现metaclass=MyType时，则代表创建类时没有使用type创建类，而是使用自定义的MyType创建类，可以通过在__new__方法中添加说删除类方法或类变量。
• 类中获取父类中指定了metaclass，全部都是由metaclass创建的类。

class MyType(type):
    def __new__(cls, name, bases, attrs):
        # print(name, bases, attrs)
        del attrs['v1']    # 删除'v1'
        attrs['dex'] = "xxxx"    # 添加'dex'
        xx = super().__new__(cls, name, bases, attrs)
        return xx


# Foo = MyType("Foo", (object,), {"v1": 123, "func": lambda self: 999})
class Foo(object, metaclass=MyType):
    v1 = 123

    def func(self):
        pass
        
class Info(Foo):    # Info类也是由MyType创建的
    V2 = 456


print(Foo.func)
print(Foo.dex)
print(Foo.v1)    # 程序报错

2.2 object、type说明

• object，所有类的就基类（公共功能，都写在里面）
• type，创建类

class Foo(object):
    name = 'abc'
    age = 20

    def func(self):
        return 999
        
obj = Foo()
print(obj.__str__())    # <__main__.Foo object at 0x0000029FFFAEC340>

3.drf序列化简要流程

class SerializerMetaclass(type):
    def __new__(cls, name, bases, attrs):
        data_dict = {}
        for k, v in list(attrs.items()):  # {"v1":123,"v2":123,"v3":123}
            if isinstance(v, int):
                data_dict[k] = attrs.pop(k)
        attrs['_declared_fields'] = data_dict
        return super().__new__(cls, name, bases, attrs)


class BaseSerializer(object):
    pass


class Serializer(BaseSerializer, metaclass=SerializerMetaclass):
    pass


class ModelSerializer(Serializer):
    pass


class UserSerializer(ModelSerializer):
    v1 = 123
    v2 = 456
    v3 = "哈哈哈"


print(UserSerializer.v3)
print(UserSerializer._declared_fields)